A Continuous β-NiAl Layer Forming at the Interface of a MCrAlY and CMSX-4

Abstract

Abstract.A large test sample of single crystal superalloy (CMSX-4) deposited with a MCrAlY coating of γ and β phases was subjected to a thermal-cycling fatigue (TCF) test at 1100 °C for about 300 cycles. Near the coating-substrate interface where an inner β-depletion zone often develops in the coating for other superalloy-MCrAlY systems, a continuous β-layer was formed instead for this particular system after the TCF test. The formation of the β-layer was related to the accumulation of Al at the interface. Simulations using an oxidation-diffusion model were carried out on this and a number of other superalloy-MCrAlY systems. It was derived that the formation of the β-layer at the interface was likely due to the high Al activity of CMSX-4 which resisted the inward diffusion of Al from the coating. The simulation results also indicated a positive effect provided by the formation of the β-layer on the coating's oxidation resistance.

Microstructure and lifetime of Hf or Zr doped sputtered NiAlCr bond coat/7YSZ EB-PVD TBC systems

“…The values of the nominal composition of Ta-containing NiCoCrAlY as well as the IN100, M247LC SX, and CMSX-4 superalloys are included as part of the same table [21,30,31]. It is well known that some elements, such as Ti, Ta, Mo, W, Hf and Re play an essential role in the diffusion processes of coated superalloys when exposed at high temperatures irrespective of the type of BC [14,21,26]. In the present cases, the main goal is to study the effects e.g., of Ta from the BC or specific elements from the substrates on the microstructural and chemical evolution of the TBCs through different processing steps.…”

“…Previous reports have been focused on oxidation effects (e.g., weight gain, lifetime under furnace cycling tests) as well as oxide scales and bond coat characteristics [14,[22][23][24]. Moreover, few investigations have been conducted to understand the interplay of Ta with Ti, Hf, Re, among other elements from the used superalloys, and the way it affects the microstructure and diffusion phenomena between the bond coat and the substrate, especially at their interface [25][26][27]. In this contribution, the effect of the chemical composition of IN100, CMSX-4 and M247LC SX superalloys on the microstructural and chemical evolution of a NiCoCrAlYTa BC through different processing stages and thermal cycling tests is presented and discussed.…”